Username and password authentication for WIF (Wind

We have two existing legacy web applications, one for the intranet using windows authentication within the domain, and one internet application, performing a custom web forms username + password based authentication. Now a new web applications is developed and will be available in the internet to both internet and intranet users, handling both authentication models. Therefore we decided to use WIF. We're going for ASP.NET 4.5 MVC 4 on Windows Server 2012.

The intranet authentication shouldn't be a problem as we can use ADFS 2.0 here.

But we currently have no clue how to solve the username + password authentication. It looks like we need to develop a custom UserNameSecurityTokenHandler to authenticate users which provide username + password information which is verified against our custom membership provider. But I need some assistance with the whole workflow...

Assume that we have a custom login page for internet users; and assume that we managed to route internet users to this login page (in ASP.NET MVC), what's the missing part from here to a valid token? How would the form or the MVC controller action which received the provided username + password proceed to trigger the configured WIF identity provider?

The most elegant solution would be to create another STS for the external users and have ADFS trust this as an identity provider:

External users will be redirected to the IdP STS that would use the usr/pwd database. Internal users will authenticate through ADFS directly (against AD).

In this scenario, ADFS is acting both as an IdP and a Federation Provider.

For this to work you need both ADFS and the IdP (and the app) exposed to the internet. An STS you can use that leverages membership is IdentityServer, which is open source and you can of course customize for your needs.

With this architecture you don't need any special customizations/extensions in the app. You will need to handle "home realm discovery" though. Which is the process of knowing where to authenticate users on (e.g. intranet vs. extranet). Presumably, you might have different URLs, etc.